RESUMEN
In the present investigation, we report the transformation of alpha-LiVOPO 4 to alpha-Li 3V 2(PO 4) 3, leading to an enhancement of capacity. The alpha-LiVOPO 4 sample was synthesized by a sol-gel method, followed by sintering at 550-650 degrees C in a flow of 5% H 2/Ar. The structural transformation of a triclinic alpha-LiVOPO 4 structure to a monoclinic alpha-Li 3V 2(PO 4) 3 structure was observed at higher sintering temperatures (700-800 degrees C in a flow of 5% H 2/Ar). The alpha-Li 3V 2(PO 4) 3 phase was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and X-ray absorption near edge spectrum (XANES) techniques. The valence shift of vanadium ions from +4 to +3 states was observed using in situ XANES experiments at V K-edge. The structural transformation is ascertained by the shape changes in pre-edge and near edge area of X-ray absorption spectrum. It was observed that the capacity was enhanced from 140 mAh/g to 164 mAh/g via structural transformation process of LiVOPO 4 to Li 3V 2(PO 4) 3.
RESUMEN
In this paper, we report the synthesis of carbon coated Li(Mn0.35Co 0.2Fe0.45)PO4 and discuss the effect of Co2P formation during the carbothermal reduction process, which enhances the electrochemical performance of cathode material for lithium ion batteries. It was observed that Co2P was favorably formed in 5% H2/Ar than in Ar atmosphere. The conductivity of Li(Mn0.35Co0.2Fe0.45)PO4/C sintered at 600-800 degrees C in 5% H2/Ar is increased as the temperature is increased. The O K-edge X-ray absorption near edge spectrum (XANES) demonstrates that content of hole carriers is increased in Li(Mn0.35Co0.2Fe0.45)PO4/C as the amount of Co2P increased. We also observed that the capacity of Li(Mn0.35Co0.2Fe0.45)PO4/C is increased with sintering temperature, and it exhibited a maximum capacity of 166 mAh/g at 700 degrees C. It was found that the enhancement in the discharge capacity of sintered Li(Mn0.35Co0.2Fe0.45)PO4/C was as a result of its higher electrical conductivity under 5% H2/Ar atmosphere as compared with Ar atmosphere.
RESUMEN
The synthesis of platinum nanoparticle loaded LiCoO2 (Pt-LiCoO2) was carried out successfully by an impregnation method followed by sintering at different temperatures. The catalytic role of Pt-LiCoO2 composite in hydrogen generation during hydrolysis of sodium borohydride (NaBH4) was studied for fuel cell applications. X-ray diffraction (XRD), transmission electron microscopy (TEM), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) have been used to elucidate the structural and catalytic properties of Pt-LiCoO2. It was found that the 15 wt % of Pt nanoparticles on LiCoO2 sintered at 450 degrees C support showed the maximum efficiency for the catalysis reaction of hydrogen production. X-ray absorption near edge structure (XANES) analysis and extended X-ray absorption fine structure (EXAFS) analysis using a synchrotron radiation source were performed to carry out ex situ measurements in order to understand the mechanism of the catalytic process for the production of hydrogen during the hydrolysis of NaBH4. Co K-edge XANES showed a small percentage of cobalt in the metallic form after hydrogen generation which suggests the reduction of the cobalt during the hydrolysis of NaBH4.